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Light sensors on shabbos


Rabbi David Sperling

Elul 20, 5777
Sir, I have a vacation condo. Management just installed lights in stairwells that always stay on (lit) but that automatically increase in intensity if someone walks near them. Thus on shabbos, when i walk up stairs, I am causing lights to increase ie get even lighter (I’m not turning them on bc they are already on). Is this a problem on shabbos. Related issue: walking in my neighborhood, some houses have light sensers that turn on lights when someone walks by, is this a problem on shabbos? thanks for your response I.Sassover
Shalom, Thank you for your question. Ideally one should not install such light sensors, as their use on Shabbat raises issues of the use of electricity – albeit in an indirect way. However, in today's world the question you raise is quiet common – and almost impossible to avoid. In such situations (where such lights are already installed, and one cannot easily avoid them), it is permitted to walk near them, as long as your intent is not to specifically turn on (or turn up) the lights, and that you do not use the light that has been turned on directly. So, to walk into the stairwell so that the lights will turn on in order to read something, or run up the stairs quickly (which would be hard to do in the dark) is forbidden. But to walk up the stairs in order to get to your house, in the same way you would without the lights turning on (or up), is permitted. The same is true of walking down the street where light sensors turn on street lighting. (For your halachic knowledge let me add – your situation is slightly better than regular light sensors, in that the light is already on, and all that is happening is an increase in voltage. This is less of a Shabbat labour than a regular sensor that turns the light on completely. None the less, these types of sensors should also be avoided where possible – but, as we wrote above, when they have been installed and cannot be easily avoided, one may walk past them). Blessings.
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